(1) Field of the Invention
The present invention relates to an improvement of a process for preparing lactamide. More specifically, the present invention relates to an industrially advantageous process for efficiently preparing lactamide, which can be used as a raw material for various kinds of organic products such as lactates and lactic acid which are useful as materials for organic synthesis and solvents, by a hydrating reaction of lactonitrile.
(2) Description of the Related Art
It is known that lactamide can be converted into a lactate by an amide-ester exchange reaction with a formate or by an alcoholysis, and this lactate can then be subjected to a hydrolysis treatment to thereby prepare lactic acid. Needless to say, the above-mentioned lactate and lactic acid are useful as materials for organic synthesis and solvents, and particularly, lactic acid is useful as a mildewproofing agent and a raw material of a biologically degradable polymer. Furthermore, the lactate can be utilized as a raw material for manufacturing an acrylate with the aid of a dehydrating reaction, and so it is industrially important and applicable to many uses.
As understood from the above, lactamide is an extremely important compound as a raw material for the lactates, lactic acid and various organic products.
Now, it has been suggested to use b type manganese dioxide as a catalyst in a hydrating reaction of acetone cyanhydrin (the specification of U.S. Pat. No. 4018829). As techniques for preparing manganese dioxide for hydrating acetone cyanhydrin, there are disclosed a method comprising the step of introducing zinc thereinto, a method comprising the step of reducing potassium permanganate with hydrochloric acid (Japanese Patent Application Laid-Open Nos. 57534/1988 and 57535/1988), and a method comprising the step of reducing a permanganate with hydrazine, a hydroxycarboxylic acid or its salt (Japanese Patent Application Laid-Open No. 269666/1994).
On the other hand, it has been suggested that manganese dioxide is used as a catalyst in a hydrating reaction of lactonitrile belonging to a cyanhydrin like acetone cyanhydrin mentioned above (specifications of Japanese Patent Publication No. 47822/1986 and U.S. Pat. No. 5,175,366). In addition, there is disclosed a hydrating reaction of lactonitrile in the presence of a catalyst comprising manganese dioxide prepared by a method which comprises reducing a permanganate with a polyhydric alcohol, or a method which comprises reducing it with a polyvalent carboxylic acid or its salt (Japanese Patent Application Laid-Open Nos. 19637/1997 and 24275/1997).
However, when manganese dioxide prepared by either of the above-mentioned method is directly used as it is as the catalyst for the hydrating reaction of lactonitrile, there is a problem that its catalytic activity rapidly deteriorates in a short period of time, and for this reason, the aforesaid techniques have not been put to practical use so far.